Content-Length header
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The HTTP Content-Length header indicates the size, in bytes, of the message body sent to the recipient.
Content-Length is limited in that the message size must be known up front, before sending the headers, which is a problem when content is dynamically generated or streamed.
- In HTTP/1.0, it is required.
- In HTTP/1.1, it could be replaced with
Transfer-Encoding: chunkedfor responses sent out in parts as its size is calculated. - In HTTP/2,
Content-Lengthis redundant, because the content length may be inferred from DATA frames. It may still be included for backwards compatibility.
| Header type | Request header, Response header, Content header |
|---|---|
| Forbidden request header | Yes |
| CORS-safelisted response header | Yes |
Syntax
http
Content-Length: <length>
Directives
<length>-
The length in octets.
Specifications
| Specification |
|---|
| HTTP Semantics # field.content-length |
Browser compatibility
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Content-Length
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CORS-safelisted response header
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Legend
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- Full support
- Full support